1. Field of Invention
This invention relates to an optical admission scheme using an optical carrier drop/add transceiver.
2. Description of Related Art
Communication information can be routed between customers using various different kinds of communication networks, including optical fiber communication networks. One type of optical network uses a ring configuration to send information to and receive information from subscribers. In a ring network, nodes which route, terminate, or otherwise process signals are connected by optical communication links, such that the links form a single loop. Optical ring networks may employ wavelength division multiplexing (WDM), in which a plurality of communication channels, in the form of discrete wavelength, are combined into a single optical transmission medium, such as an optical fiber.
Traffic on such WDM optical rings may be hubbed, in which case all wavelength channels originate and/or terminate at a central hub node, while one or more wavelength channels are supplied to each subscriber by corresponding add/drop modules that are located at remote nodes of the ring. Each of the add/drop modules also integrates communication information provided by a corresponding subscriber into the optical communication system so that the subscriber""s communication information is returned to the hub node. For traffic which is not hubbed, a wavelength channel can originate at a first subscriber, be integrated into a communication link by a first add/drop module, be transported to a second add/drop module capable of selecting the corresponding wavelength, and be terminated by a second subscriber. More complex mesh networks can be constructed by combining rings which intersect at one or more nodes.
As the traffic level of large users approaches the line rate for a single wavelength of light on a network operator""s ring, there is an incentive to permit the user to make a direct optical connection to the network ring. To provide the communication channels to a subscriber, each of the add/drop modules filter out a particular wavelength channel by either selecting or filtering, a specific wavelength channel. Thus, the add/drop modules are capable of selecting a set of particular wavelength channels from the plurality of channels present on the optical network.
Permitting a subscriber to make a direct optical connection to the network ring can increase efficient communication between subscribers. For example, two subscribers sharing a direct optical connection on a network ring can communicate in a native or custom format, rather than the conventional manner of requiring each subscriber to convert to and from an optical network service provider""s mandatory format. Conversion to and from a mandatory standard format can require the use of costly conversion equipment and can incur inefficiencies in the communication between nodes.
However, the advantages of permitting a subscriber to make a direct optical connection to an optical network ring can be offset by the network""s vulnerability to subscriber errors which are beyond the control of the optical network service provider. For example, a direct optical connection requires the subscriber to receive and transmit data on a very specific channel (wavelength) of the optical network ring. Variations caused by changing conditions, such as temperature, make constant operation at a specific channel difficult to monitor and control. Furthermore, using a direct connection with the optical network ring, any errors introduced by the subscriber, such as incorrect operating wavelengths, are beyond the control of the optical network service provider, and may corrupt not only the subscriber""s communications, but also communications in neighboring wavelength channels. These problems are compounded by the fact that the wavelength control must be exercised at each wavelength and at each node.
The invention provides an optical carrier drop/add transceiver in which optical carriers are generated by the network operator at controlled locations and are shared by several users. That is, the same optical carrier both drops traffic from the optical network ring and adds traffic to the optical network ring. An optical carrier signal is received by the transceiver and is subsequently optically split into a first and second optical signal. The first optical signal can be converted into an electrical signal for processing by the subscriber (i.e., data out). The electrical signal corresponding to the first optical signal is additionally inverted by the transceiver. The inverted electrical signal is subsequently used to modulate the second optical signal in order to suppress the data, and thereby create a nominally cw signal. Since new data can now be impressed on this nominally cw signal, it is convenient to think of it as an xe2x80x9coptical chalkboardxe2x80x9d that has been reconstituted from the original signal. The subscriber""s data is then modulated onto this nominally cw signal, and sent into the optical network. As a consequence, the network subscriber controls the format and protocols of the data traffic on the optical network, while the optical network service provider controls the optical carrier wavelengths, which are of primary concern to maintain organization and efficiency on the optical network. Thus, in essence this provides an admission scheme for the network operator to insure that only the correct wavelengths are admitted to the network without the need to impose format restrictions.
In the admission scheme of the present invention, the optical network service provider originates the network""s optical carriers, either at the hub or node, which carry the subscriber""s data. Therefore, the optical network service provider is insured adequate network control because the optical network service provider, whose primary concern is network integrity, completely controls the channels (wavelengths) over which the subscribers transmit/receive data. Additionally, the network subscriber, whose primary concern is data transport, controls the data format and the protocols by which the data is transmitted since the network subscriber imposes their own modulating signals on the light which the network service provider has supplied.